Valuable materials in the ground, such as ores or oil deposits, can be detected directly or indirectly using suitable airborne gravity gradiometers. Such valuable materials usually have a density other than that of surrounding materials, which results in a local variation or “anomaly” in gravity gradient that is detectable by the gravity gradiometer when the gravity gradiometer is flown over a terrain including the valuable material. The gravity gradient anomaly is usually extremely small and its detection requires high precision instrumentation. The valuable material often is below the surface of the terrain and the gravity gradient anomaly is proportional to 1/r3 (r: distance from the centre of the valuable material to a detector of the gravity gradiometer).
Topographical changes of the surface of the terrain also cause variations in gravity gradient and these variations may be larger than the gravity gradient anomalies arising from the valuable material, as the surface of the terrain is closer to the airborne gravity gradiometer than the (usually deeper) targets. It is consequently desirable to correct gravity gradiometer measurements for these terrain effects in order to facilitate recognition of anomalies from deeper sources.
US patent application publication number US 20100094556 discloses a method of correcting gravity gradient data. The measured gravity gradient data is integrated in the time domain and then corrected for terrain effects. The present invention used an alternative approach that provides further improvement.